1. Field of the Invention
The present invention relates in general to DC-DC switching regulators, and more particularly to a system and method for adaptive current limit setting of a switching regulator to improve efficiency at lower load levels.
2. Description of the Related Art
A DC (direct current) to DC switching regulator converts an unregulated input DC voltage to a regulated output voltage or otherwise converts voltage from one voltage level to another. A switching regulator typically includes an inductor, a capacitor, a switch network (including at least one switch), a rectifier or rectifying element, a feedback network and a modulator. The modulator monitors one or more sense signals via the feedback network and adjusts a pulse control signal used to control the switch network. The switch network switches voltage applied across the inductor which is used as a storage device to transfer energy from the input voltage to an output voltage stored on the capacitor.
The feedback network is configured to sense various parameters of operation depending upon the particular configuration to develop and provide the sense signals to the modulator for purposes of control. For example, the parameters typically include the output voltage in which the modulator adjusts the pulse control signal to maintain the output voltage within a regulation voltage range above and below a target or desired nominal voltage level VNOM. The pulse control signal may be implemented as a pulse width modulation (PWM) signal in which the modulator adjusts the duty cycle of the PWM signal.
Another parameter that may be monitored by the feedback network is the peak current level of current through the inductor. In a boost converter, for example, a switch is turned on to apply the input voltage across the inductor to cause inductor current to increase to store energy in the inductor. When the current reaches a peak level, the switch is turned off and the stored energy in the inductor tends to collapse and the voltage polarity changes such that it adds to the input voltage. The rectifying element coupled between the inductor and the output turns on to charge the output voltage until the current decreases to zero or some other predetermined level. The cycle then repeats during normal operation.
Power consumption and efficiency is of utmost importance in portable and/or battery-powered applications or in energy monitoring or conversion devices (e.g., used for solar energy applications or the like). The switching regulator is used to convert the voltage level of an input voltage of a battery or a monitoring device or a conversion device or the like to a regulated output voltage useful for electronic devices or measurement devices and the like. The conversion efficiency of the switching regulator is an important aspect of the power consumption and efficiency of the overall system.